The present invention relates to direct adhesion of materials and, more particularly, to improving the adhesion of a film of a material to an electrical insulator by irradiating the interface between the surfaces with high energy ions.
Though the invention is of general application in its ability to enhance the adhesion of any material, whether conductor or insulator, to an insulator substrate, there are many insulator substrates that do not form stable, adherent bonds even with pretreatment of the surface or use of adhesives. For example, it is very difficult to bond metal films such as gold or silver to refractory substrates such as quartz. It is also difficult to permanently apply metal or even printing inks to synthetic polymeric materials such as hydrocarbon polymers, for example polyethylene or polyfluorocarbon materials such as Teflon (polytetrafluoroethylene). Metal films applied to these surfaces by evaporation form very weakly adherent bonds and the films can be readily peeled off the surfaces.
There are many applications where the service life of the device is severely limited by the nonpermanence of a coating on an insulator, for example, low and high powered laser mirrors or mirror coatings used in ordinary and celestial telescopes. Many small and intricately shaped devices such as ferrite heads for reading tapes and magnetically coded discs are difficult to coat. Other products currently being produced and/or developed that require bonding of a thin film of metal to an insulator substrate are printed circuit boards, integrated circuits and semiconductors such as photovoltaic cells.